It has been a goal in wireless communications to devise a mechanism to enable a wireless transmit/receive unit (WTRU) to place or receive a communication during an ongoing session without service interruption. For example, in a Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) scenario, a goal has been to devise a mechanism to enable a WTRU, while it is connected to a packet switched (PS) domain of an Evolved Universal Terrestrial Radio Access Network (E-UTRAN), to place (i.e., originating) or receive (i.e., terminating) circuit switched (CS) services or vice versa. Examples of CS services may include at least such services as a CS voice call, a short message service (SMS), location services, or supplementary services. The initiation of a CS session during an ongoing PS session by a WTRU is referred to as CS fallback (CSFB).